Variable Weight?

Pressure in or on what?
Pressure in a liquid or gas is going to applied somewhat differently from say clamping pressure in a glueing jig.

C'mon we are not telepathic, I'm sure you know what you mean, but try reading your post from our position.

Del, maybe I should change my user name to Gigo ?

_{C'mon we are not telepathic, I'm sure you know what you mean, but try reading your post from our position.}

Not so easy, huh?

Del, Aparently I see things in a different way than you do. I am more interested in helping than hasslling the person asking for a few words of wisdom. It looks to me that an Engineer with exsperience should be able to understand or relate the questions and if not be able to ask for a clarification instead of blasting the one in need of your wisdom. We may not all be as educated as you but its how you use your knowledge that matters atleast that's how you will be viewed and thought of. Its as if your only objective is to amass numbers even at the exspence of others. It wouldn't surprise me if people deleted CR4 from their favorite places and looked for their answers elsewhere when they are chastised for not meeting your needs, an Engineer I think not. I hope you will have a pleasent new year and continue your education for it appears you missed or slept through a few classes. And as far as Off Topic goes you should take time to review a few of your 2000+ post before ever thinking of doing such a thing.

Maybe you should take the time to click on my profile and see all the blogs and stuff I have contributed to this site.

Yes, I do actually do stuff, provide usefull answers and a little entertainment too.

The questions posed in my post are perfectly valid. Rubber bands can apply varying pressure to a glueing jig, but wouldn't be appropriate to pressurise a water line, whereas a peristaltic pump would satisfy the latter requirement but not the former.
And you have the gall to say I'm the one not being helpful?

Hang on a minute!...you say
I am more interested in helping than hasslling the person ..
Yeh right...but you don't answer their question.
There is an expression 'all mouth and trousers'... I think that sums your post up rather nicely.

Del

Apparently the peristaltic pumps you build are an universal solution. Why not a bow? It is a spring also

Guest

look at the the OP

There were no questions it sounding more like a statement.

Its like you go to a doctor and just say it hurts...........and thats it

What hurts? where? when did it start? what where you doing?....ect......

refine it it more, and if Del (or any other member of CR4) has a solution, he'll (we'll) post it.

phoenix911

absolutely awesome.

Please note that the OP could have a bit of a problem with following our idea of procedure. He could be and I think he is quite insecure to even handle the English language. He is getting all this flack and could be quiet in need of an answer!

At least we have tried and if he thinks we are all arrogant bastards, let it rest. He could be reading this and discovering that the ignorance is on his side. What ever, no one is going to get damaged, really!

All the best, Ky.

Yes, but in amoungst all the criticism, you still managed to proved some essential data that has been missing from other posts!

who in the hell voted that as "off topic" ?

Seriously - off topic? That response deserves a Peabody and a Pulitzer!

Assuming that you want a pressure to be applied on something pl use a hydraulic cylinder / press you will have a lot of them, ask the manufacturer to put a pressure controller and the gauge can be calibrated in terms of pressure (Kgwt)

We have a large one at our place - the pressure is controllable (thereby the load is controlled) only problem is it is a 100T press and you need a 1/4T.

What you want is regularly done in a tensile tester (only it pulls insted of pushing)

Also if you want it cheaper, just fabricate one with a simple mechanical spring (only 250 Kg) the shape of the structure you can adjust to your work piece and loading can be done by a simple nut+washer combination, calibrate the needle to weight (regularly done in spring balance, only here again tensile instead of compressive)

If it is variable pressure you want - what us the fluid ? gas may be a bit difficult, any oil use first method (power pack + pressure controller)

DrMogbl, On machinery that I installed and maintained for many years the evolution went from stacks of iron weights to pneumatic cylinders and regulators to accomplish the same thing. Very efficient & time saving in making adjustments or trouble shooting. Our application was in tensioning clouth bands that pulled the product through the machiine and the tension was very critical. Wish you a successful 2009. J.Conway

DrMogobl -- I'm figuring you are a medical doctor, a biologist of some sort or in an area of technology that is a bit away from our world of mechanical engineering. So I'll start simple......

The easy ways to apply a known load in the range you desire are a threaded bolt, a hydraulic jack or a known weight. Any of these can act directly or through a lever system of some kind. If you need to know the actual amount of the load then you must have some way to measure it to the degree of accuracy your project requires.

For high accuracy requirements the measurement should take place as close to the point of application of the force as possible to minimize the inaccuracies due to static friction that occurs in even the simplest of mechanisms. And you will need to have a method of calibration of the weight measurement that can be verified to be several times more accurate (10 times is preferred) than the requirements of your actual measurements if your work is to be presented for critical peer review or sold into global commerce.

Simple methods of accuracy in the range of a few percent are:

High quality bourdon pressure gauge to measure hydraulic pressure which is multiplied by the area of the hydraulic cylinder to get the actual force applied.

Weights that can be calibrated on a suitable weighing scale (in many cases a bathroom scale is good enough.) Also we know the weight of water exactly at any given temperature; so an accurate volume measurement will give an accurate calibrated weight if the weight of the container is known or insignificant (say a light plastic bag).

A bolt or screw acting through a coil spring in a manner that the compressed length of the coil spring can be readily measured to within a small fraction of a millimeter. To prepare the spring for this use it can be calibrated on a small platform or bathroom scale placed on the table of a drill press and accurate measurements of length taken while loads are applied with the drill press quill. (best a 2 person job)

For better levels of accuracy purpose built force gauges are manufactured. These devices typically employ a precision coil spring and length measuring display which is calibrated in force units like kilograms in a single housing with a variety of optional mechanical components for mounting and applying the forces to be measured.

Beyond this there are a variety of more sophisticated load cells that produce an electrical signal output that needs to be processed electronically; but lend themselves well to automated data collection and recording.

Does this help you get started? Hope so.

Ed Weldon

Hi Dr Mogbl

One way you could achieve a result is to acquire a small hydraulic power pack. With it's basic equipment like pump, reservoir, filter and direction control valve all in place, you will then need to fit a proportional pressure relief valve (PPRV) on the 'P' port of the DCV and fit a suitably sized cylinder to the service lines of the DCV. You will also require a good quality gauge to fit to the cylinder supply lines.

To control the PPRV by either 4-20mA or 0-10V, use a cheap Heat/Cool controller with a digital numerical display. Calibrate your machine as desired.

If used for long duration pressing, fit a very VERY large cooler!

Simple circuit diagrams are available on the web.

Good luck with it

a container of water with a level control system will allow you to vary weight, pressure, and volume in an analog and possibly linear manner. (depending on the design of the supply/relief system)

250 kg will be too much of a container

it is application dependent.. we still need to know more of the purpose, context, input conditions, output expectations. Its all guesswork at this point to figure out what the OP wants.

250kg is only filled water in a container of 1/4 cubemeter.

open a hole at bottom, when water drop out, the weight will be change accofding to height uniformly.

like this.

Why so many OPs keep silent after an initial post ?

It is not that no ideas have come in.

Many use CR4 as a "get out of actually working" tool. They throw out some half-baked question, with way to little information to get a meaningful answer.

So, after an hour or so, with no answer that helps them, they actually have to get off of their lazy asses and do the work themselves. At which point, they have no more use for us, and their gone.

Bricktop-- I think you may be right about this; more so than I want to admit. I've tended to give some of these "guests" the benefit of the doubt assuming their English isn't all that great or that they are ordinary people trying to solve a real life technical problem for which they have no real training. Perhaps I'm just being charitable.

Why do we even bother trying to read meaning or intent into the words of some mindless idiot who chooses to remain anonymous so he can avoid the simplest courtesy of a thank you for a sincere effort to help.?

On the other hand it is kind of a personal challenge to come up with a concise explanation in simple words. .......... Sometimes CR-4 is just a computer game one plays with oneself.

Ed Weldon

sb, SB now isn't that a coincidence, do you think maybe its has to do with the amont of attitude included in the replies that may send them in someother direction for assistance in solving the problem at hand. In todays working enviroment the norm is for the engineers to stay in their Ivory Towers and dictate to the peasants what must be done. It seams as though the same ways of handling problems has followed them here not thinking that they are responding to their equals or maybe greater thans. Greater than yourself, now isn't that a thought. Good day,

Dear Guest

Yes we some times try to be sarcastic, and may be in ivory towers but if you like to go through threads (pl check them) there had been from simple (#16) to complicated (#2) all were genuine solutions.

However if as was mentioned, the final applications, budget etc are unknown, what can the persons on ivory tower or any other tower can do ?

We are not dictating terms to peasants, check thru the mails in CR4 (when we are on peasants mode, we are taking care to mark it off topic).

And in these forums at least I have seen that no body thinks about the equality/inequality/superiority of others.

Yes, on a particular subject I may seem to know more than others (as I think while writing the answer), the next few minutes burst my bubble (and I am back to earth).

Just to give an example, I am Electrical(By degree)- but am forced to alternate bet hydraulic/Mech.Metallurgist (by profession) - I can call myself jack of all.

A discussion just read before this post (SQ Cage Fuse blow out) has been what i would have thought otherwise - and as usual, exactly opposite to my conscience.

But as I think, that is also an avenue for thinking. I don't agree with the total of that logic, but will have to think about it, and this way of thinking in collaboration - not as persons of ivory towers but as humans sharing their thought what is making me addicted to this site.

Pl remove your misconception about us, and join us so that we can talk to a person (may be an avatar) but not to a no-name.

And I do not think it as an attitude, it may be he could solve it by may be one of the seeds that were planted in these discussions (only OP can tell and he is silent) but the other concepts that had been shared are may be useful for somebody of us at later date.

Hi SB

#16, SIMPLE! I could have made the description WAY more complicated and precise but.......AND here is the point:-

We all agree that the OP didn't put his question very well however, rather than waste time to ridicule the OP, why not look at it as 'more freedom of license' to expound your own 'pet solution' given that, you could hardly be wrong given the lack of original data! This is the reason for the lack of detail in #16. It was the 'first shot across the bow'. We, at CR4, would normally hope that the OP would then come back and say 'No, not that, we need to xxxxx'! We could then harden up the solution to a credable conclusion!

Just my point of view!

Sb, My sincerest appolligies for not being perfectly clear in my previous post. My reply was ment to be in agreement with you in post #35 stating the following ( Why so many OPs keep silent after an initial post ? It is not that no ideas have come in. ). To make it easy to review the kind of facts that I form my opinions around take a look at the post preceeding yours ( #25) and the two post following yours (#36 & #37). This is a good example of someone thats only purpose is to consume oxygen and takes up space, space that is only as valuable as its ocupant, in this case their ocupation of those spaces devalues all of those around them. Do you want those type of people deciding your value? I hope not. Sir you are a gentleman and a scholar and I had no intentsions of harming you in any form. It is clear that you post for the betterment of your fellow man and not at their exspence. If I ever achieve 5000+ post and my GAs are not much more than 1% then I hope to have the the courtesy to bow out graciously, for the numbers would be proof of my intensions of consuming space. To those that serve Good Day, to those whom hinder good buy.

Thanks and sorry for any misunderstanding

We do try to help but get impatient when OP is silent (and as human or fiend as the case may be get fiendish since we do not know where we are wrt the OP.

Sorry (it was #22) missed the number

But his problems could have been solved had he interacted and as you mentioned, said "no not that my requirement is this..."